refactor(verity): propagate conversion errors

Author: kvinwang

dstack/crates/dstack-verity/src/volume.rs

@@ -370,11 +370,11 @@ fn write_volume_header(out: &mut fs::File, offset: u64, root_hash: &str) -> Resu
     use std::io::{Seek, SeekFrom, Write};
 
     let root = hex::decode(root_hash).context("decoding verity root hash")?;
-    if root.len() != 32 {
-        bail!("verity root must be a 32-byte SHA-256 digest");
-    }
-
-    let header = DstackVolumeHeader::new_verity(root.try_into().expect("length checked above"))
+    let root: [u8; 32] = root
+        .as_slice()
+        .try_into()
+        .context("verity root must be a 32-byte SHA-256 digest")?;
+    let header = DstackVolumeHeader::new_verity(root)
         .encode()
         .context("encoding volume header")?;
 

dstack/guest-agent/src/bin/dstack-volume.rs

@@ -354,10 +354,10 @@ fn seed_docker(volume: &Path) -> Result<()> {
         if !source.is_dir() {
             continue;
         }
-        let target = store
-            .join("overlay2")
-            .join(layer.file_name().unwrap())
-            .join("diff");
+        let layer_id = layer
+            .file_name()
+            .context("docker layer path has no file name")?;
+        let target = store.join("overlay2").join(layer_id).join("diff");
         fs::create_dir_all(&target)?;
         if !is_mountpoint(&target)? {
             if let Err(err) = checked(